Several studies found a good correlation between prolonged GCTT measured with lactulose-[eH.sub.2]test in constipated children [13, 22] while other studies did not .
A10 ppm [eH.sub.2] increase was absent in most of our patients and, in patients in whom it was present, no correlation was found between GCTT and patient's defecation rhythm or any other clinical or treatment variables.
GCTT could only be measured in four patients (36.4%), and although it was longer for constipated children , no correlation was found between the GCTT and the time to stooling or any other nutritional complication, suggesting that the test has no clinical usefulness in the critically ill child.
Another possible factor might be a very slow GCTT (of more than 6 hours).
Therefore, according to our results, lactulose-[eH.sub.2] test does not seem to be useful to measure GCTT in children with mechanical ventilation, although the designed amendment is useful for collecting breath samples.
There are other devices for measuring GCTT in constipated children as [sup.13]C-lactose, colonic radioscintigraphy, colonic manometry capsule motility, or radiopaque markers.